Dual-phase stainless steel

ABSTRACT

A dual-phase ferritic-martensitic stainless steel includes, by weight, about 11.5% to about 12% Cr, about 0.8% to about 1.5% Mn, about 0.75% to about 1.5% Ni, 0% to about 0.5% Si, 0% to about 0.2% Mo, 0% to about 0.0025% B, Fe, and impurities. In various embodiments, the steel has a Brinell hardness (HB) and Charpy V-notch impact energy at −40° C. (CVN) such that CVN (ft-lb)+( 0.4 ×HB) is about 160 or greater. Articles of manufacture including the stainless steels also are disclosed.

BACKGROUND OF THE TECHNOLOGY

1. Field of Technology

The present disclosure relates to a dual-phase stainless steel having amicrostructure of ferrite and tempered martensite. In particular, thepresent disclosure relates to cost-effective stainless steels havingimproved hardness for abrasion-resistant and/or wear-resistantapplications.

2. Description of the Background of the Technology

Dual-phase stainless steels can exhibit a combination of desirableproperties that make them useful for a wide variety of industrialapplications, such as for oil sands extraction and in the sugarindustry. These steels are generally characterized by a microstructureof tempered martensite dispersed in a ferrite matrix.

An example of a dual-phase stainless steel is ATI 412™ stainless steel(UNS 41003), which typically contains, by weight, 11.75% chromium (Cr),0.90% manganese (Mn), 0.70% silicon (Si), 0.40% nickel (Ni), 0.030%sulfur (S), 0.020% carbon (C), 0% to 0.040% phosphorus (P), 0% to 0.030%nitrogen (N), and the balance iron (Fe) and other incidental impurities.ATI 412™ stainless steel typically has a Brinell hardness (HB) of about177 when annealed at about 766° C., and a Brinell hardness of about 258when annealed at about 843° C.

Another dual-phase stainless steel is Duracorr® steel, which contains,by weight, 11.0% to 12.5% Cr, 0.20% to 0.35% molybdenum (Mo), 0% to1.50% Mn, 0% to 1.00% Ni, 0% to 0.70% Si, 0% to 0.040% P, 0% to 0.030%N, 0% to 0.025% C, 0% to 0.015% S, and the balance Fe. Notably,Duracorr® stainless steel contains Mo as an alloying element, i.e., anintentional alloying addition, and not as an incidental impurity.Because of the rising costs of Mo, however, Duracorr® stainless steelmay be too costly for certain applications. Although Duracorr® stainlesssteel typically has a hardness of about 223 HB, it can be processed toexhibit nominal hardness of 300 HB, which grade is commerciallyavailable as Duracorr® 300 stainless steel. Duracorr® and Duracorr® 300stainless steels have largely the same composition, but the hardness ofDuracorr® 300 stainless steel varies from 260 HB to 360 HB. Theincreased hardness of Duracorr® 300 stainless steel, however, isaccompanied by a reduction in toughness. For example, the Charpy V-notchimpact energy of Duracorr® 300 stainless steel at −40° C. is only about15 ft-lb on average.

In applications requiring a stainless steels having abrasion resistanceand/or wear resistance, high hardness levels, for example, up to about350 HB, may be desirable in combination with higher toughness than isavailable from Duracorr® 300 stainless steel. Moreover, an in-servicework hardenability up to about 450-500 HB, for example, may be requiredin certain applications. Furthermore, it is desirable that any suchalloys are cost-effective.

SUMMARY

According to one non-limiting aspect of the present disclosure, anembodiment of a high-hardness dual-phase ferritic-martensitic stainlesssteel is described. The stainless steel comprises, by weight, about11.5% to about 12% Cr, about 0.8% to about 1.5% Mn, about 0.75% to about1.5% Ni, 0% to about 0.5% Si, 0% to about 0.2% Mo, 0% to about 0.0025%B, Fe, and impurities. In certain non-limiting embodiments, thestainless steel according to the present disclosure exhibits Brinellhardness (HB) and Charpy V-notch impact energy at −40° C. (CVN) suchthat CVN (ft-lb)+(0.4×HB) is about 160 or greater.

According to another non-limiting aspect of the present disclosure, anembodiment of an article of manufacture including a high-hardnessdual-phase ferritic-martensitic stainless steel is described. Thestainless steel comprises, by weight, about 11.5% to about 12% Cr, about0.8% to about 1.5% Mn, about 0.75% to about 1.5% Ni, 0% to about 0.5%Si, 0% to about 0.2% Mo, 0% to about 0.0025% B, Fe, and impurities.According to certain non-limiting embodiments of the article, thestainless steel exhibits Brinell hardness (HB) and Charpy V-notch impactenergy at −40° C. (CVN) such that CVN (ft-lb)+(0.4×HB) is about 160 orgreater.

BRIEF DESCRIPTION OF THE DRAWING

Features and advantages of the stainless steels and articles ofmanufacture described herein may be better understood by reference tothe accompanying drawing in which:

FIG. 1 is a graph plotting Brinell hardness and Charpy V-notch impactenergy of non-limiting embodiments of stainless steels according to thepresent disclosure in comparison to certain conventional steels.

The reader will appreciate the foregoing details, as well as others,upon considering the following detailed description of certainnon-limiting embodiments of stainless steels and articles of manufactureaccording to the present disclosure. The reader also may comprehendcertain of such additional details upon making or using the stainlesssteels and articles of manufacture described herein.

DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS

In the present description of non-limiting embodiments and in theclaims, other than in the operating examples or where otherwiseindicated, all numbers expressing quantities or characteristics ofingredients, alloys, and articles, processing conditions, and the likeare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, any numericalparameters set forth in the following description and the attachedclaims are approximations that may vary depending upon the desiredproperties one seeks to obtain in the stainless steels and articles ofmanufacture according to the present disclosure. At the very least, andnot as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as set forth herein supersedes anyconflicting material incorporated herein by reference. Any material, orportion thereof, that is said to be incorporated by reference herein,but which conflicts with existing definitions, statements, or otherdisclosure material set forth herein is only incorporated to the extentthat no conflict arises between that incorporated material and theexisting disclosure material.

The present disclosure, in part, is directed to cost-effectivedual-phase ferritic-martensitic stainless steels having advantageoushardness and which are suitable for use in various applicationsrequiring abrasion resistance and/or wear resistance. In particular,certain embodiments of dual-phase ferritic-martensitic stainless steelsaccording to the present disclosure comprise, by weight, about 11.5% toabout 12% Cr, about 0.8% to about 1.5% Mn, about 0.75% to about 1.5% Ni,0% to about 0.5% Si, 0% to about 0.2% Mo, 0% to about 0.0025% B, Fe, andimpurities. In certain embodiments, the stainless steels exhibit Brinellhardness (HB) and Charpy V-notch impact energy at −40° C. (CVN) suchthat the following is satisfied: CVN (ft-lb)+(0.4×HB) is about 160 orgreater.

Cr may be provided in the alloys of the present disclosure to impartcorrosion resistance. A Cr content of about 11.5% (by weight) or moremay be required to provide adequate corrosion resistance. On the otherhand, excessive Cr may undesirably (1) stabilize the ferrite phaseand/or (2) embrittling phases such as the sigma phase. Accordingly,certain embodiments of the stainless steels according to the presentdisclosure include a Cr content of about 11.5% to about 12%, by weight.

Mn may be provided in the alloys of the present disclosure to improvework hardenability. A Mn content of about 0.8% (by weight) or more maybe required to achieve the desired work hardening effects. On the otherhand, excessive Mn may undesirably segregate during processing of thestainless steels. Accordingly, certain embodiments of the stainlesssteels according to the present disclosure include a Mn content of about0.8% to about 1.5%, by weight. In certain other embodiments, the Mncontent of the stainless steels may be about 1.0% to about 1.5%, byweight. In certain embodiments of the stainless steels according to thepresent disclosure, the addition of Mn in combination with the additionof other alloying elements can advantageously affect work hardenabilitysuch that the steels attain a hardness of about 450 HB or greater.

Ni may be provided in the alloys of the present disclosure to helpstabilize the martensitic phase of the dual-phase (martensitic-ferritic)alloys. A Ni content of about 0.75% by weight or more may be required toprovide a material including higher levels of martensite than inDuracorr® 300 stainless steel. Without intending to be bound to anytheory, the nickel content of the alloys may promote hardness of thealloys' martensite phase by stabilizing austenite formation during heattreatment, allowing more time for carbon diffusion. On the other hand,due to the high cost of Ni, it may be desirable to limit the Ni content.Accordingly, some embodiments of the steels according to the presentdisclosure include a Ni content of about 0.75% to about 1.5% (by weight)to provide a cost-effective dual-phase stainless steel with highhardness levels up to about 350 HB, in combination with higher toughnessthan is typical of Duracorr® 300 stainless steel. In furtherembodiments, the Ni content of stainless steels according to the presentdisclosure may be about 1.0% to about 1.5%, by weight.

In certain embodiments of the stainless steels according to the presentdisclosure, the level of Si may be limited to (1) destabilize theferritic phase of the dual-phase stainless steels and/or (2) avoidembrittling phases such as the sigma phase. Accordingly, certainembodiments of the steels according to the present disclosure include 0%to no more than about 0.5% Si, by weight.

In certain embodiments of the stainless steels according to the presentdisclosure, the level of Mo may be limited to (1) destabilize theferritic phase of the dual-phase stainless steels and/or (2) avoidembrittling phases such as the sigma phase. Accordingly, certainembodiments of the steels according to the present disclosure include 0%to no more than about 0.2% Mo, by weight. In certain other embodimentsof the steels according to the present disclosure, the Mo concentrationis 0% to no more than about 0.1%, by weight

B may be provided in the dual-phase stainless steels of the presentdisclosure to improve martensite hardness. Certain embodiments of thesteels according to the present disclosure include 0% to about 0.0025%B, by weight. In certain embodiments of the steels, the B content may beabout 0.002% to about 0.0025%, by weight.

Incidental elements and impurities in the disclosed alloys may include,for example, one or more of C, N, P, and S. In certain embodiment of thestainless steels according to the present disclosure, the total contentof these elements is no more than 0.1%, by weight. In certainembodiments, C may be present in the steels disclosed herein in anamount no more than 0.025%, by weight. In certain embodiments, S may bepresent in the steels disclosed herein in an amount no more than 0.01%,by weight. In certain embodiments, N may be present in the steelsdisclosed herein in an amount no more than 0.03%, by weight. Incidentallevels of various metallic elements also may be present in embodimentsof alloys according to the present disclosure. For example, certainnon-limiting embodiments of alloys according to the present disclosuremay include up to 0.25% copper (Cu), by weight.

According to certain non-limiting embodiments, dual-phaseferritic-martensitic stainless steels according to the presentdisclosure comprise by weight: about 11.5% to about 12% Cr; about 1.0%to about 1.5% Mn; about 1.0% to about 1.5% Ni; 0% to about 0.5% Si; 0%to about 0.1% Mo; 0% to about 0.0025% B; 0% to about 0.025% C; 0% toabout 0.01% S; 0% to about 0.03% N, Fe, and impurities. In certainembodiments, the stainless steels further comprise P. In certainembodiments, the total concentration of C, N, P, and S is no greaterthan about 0.1%, by weight. In certain embodiments, the concentration ofB in the steels is about 0.002% to about 0.0025%, by weight. In certainembodiments, the steels include no more than 0.25% Cu, by weight.

According to certain non-limiting embodiments, dual-phaseferritic-martensitic stainless steels according to the presentdisclosure consist essentially of, by weight: about 11.5% to about 12%chromium; about 0.8% to about 1.5% manganese; about 0.75% to about 1.5%nickel; 0% to about 0.5% silicon; 0% to about 0.2% molybdenum; 0% toabout 0.0025% boron; 0% to about 0.025% carbon; 0% to about 0.01%sulfur; 0% to about 0.03% nitrogen; optionally at least one of copperand phosphorus; iron; and impurities.

According to certain non-limiting embodiments, dual-phaseferritic-martensitic stainless steels according to the presentdisclosure consist essentially of, by weight: about 11.5% to about 12%chromium; about 1.0% to about 1.5% manganese; about 1.0% to about 1.5%nickel; 0% to about 0.5% silicon; 0% to about 0.1% molybdenum; 0% toabout 0.0025% boron; 0% to about 0.025% carbon; 0% to about 0.01%sulfur; 0% to about 0.03% nitrogen; optionally at least one of copperand phosphorus; iron; and impurities.

According to certain non-limiting embodiments, dual-phaseferritic-martensitic stainless steels according to the presentdisclosure consist of, by weight: about 11.5% to about 12% chromium;about 0.8% to about 1.5% manganese; about 0.75% to about 1.5% nickel; 0%to about 0.5% silicon; 0% to about 0.2% molybdenum; 0% to about 0.0025%boron; 0% to about 0.025% carbon; 0% to about 0.01% sulfur; 0% to about0.03% nitrogen; optionally at least one of copper and phosphorus; iron;and impurities.

According to certain non-limiting embodiments, dual-phaseferritic-martensitic stainless steels according to the presentdisclosure consist of, by weight: about 11.5% to about 12% chromium;about 1.0% to about 1.5% manganese; about 1.0% to about 1.5% nickel; 0%to about 0.5% silicon; 0% to about 0.1% molybdenum; 0% to about 0.0025%boron; 0% to about 0.025% carbon; 0% to about 0.01% sulfur; 0% to about0.03% nitrogen; optionally at least one of copper and phosphorus; iron;and impurities.

For a given steel, hardness is generally inversely related to toughness.In the present disclosure, Brinell hardness (HB) is the primary measureof hardness, and Charpy V-notch impact energy at −40° C. (CVN) is theprimary measure of toughness. Referring to FIG. 1, for certainembodiments of the steels according to the present disclosure, CVN(ft-lb)+(0.4×HB) of the steels is about 160 or greater. In certainembodiments of the steels according to the present disclosure, hardnessis about 300 HB or greater, and CVN is about 50 ft-lb or greater. Incertain embodiments, the steels according to the present disclosure havean in-service work hardenability up to a hardness of about 450 HB orgreater.

Examples

Table 1 includes the compositions and certain properties of anembodiment of the dual-phase ferritic-martensitic stainless steelsaccording to the present disclosure and of conventional ATI 412™stainless steel and conventional Duracorr® 300 stainless steel. Heats ofthe three alloys listed in Table 1 were melted into slabs weighing about15,000 lb and rolled at a temperature of about 1950° F. to producematerial about 6 mm thick. Following the rolling process, the steelswere annealed at 766° C. or 843° C., for 15 minutes, and air cooled.

The mechanical properties of the experimental steel embodiment listed inTable 1 were measured and compared to those of the two listedconventional steels. The Brinell hardness and CVN at −40° C. (ft-lb) areshown in Table 1 for the three alloys. The tensile tests were conductedaccording to the American Society for Testing and Materials (ASTM)standard A370 at room temperature, using a tungsten carbide ballindenter, on samples measuring about 5 cm in gauge length and about 0.5cm in thickness. The Charpy tests were conducted according to ASTMstandard A370 and E23 at about −40° C. on transverse samples measuringabout 10 mm×2.5 mm. Because these samples are considered subsize perASTM-A370, the measured impact energy was converted to standard sizespecimen values in Table 1.

As shown by the experimental results in Table 1, the experimental steelsample of the present disclosure exhibited very favorable hardness andtoughness (CVN impact energy) relative to the conventional alloys. Thiswas particularly unexpected and surprising. Commercially availablealloys providing comparable hardness and toughness typically are carbonsteels, which would not withstand corrosive environments.

In certain possible non-limiting embodiments, dual-phase stainlesssteels according to the present disclosure are prepared usingconventional stainless steel production practices including, forexample, melting of starting materials in an electric furnace,decarburization via AOD, and casting to an ingot. Ingots may be cast,for example, by continuous casting or ingot pouring. In certainembodiments, the cast material may be heat treated (austenitized) orsold as-rolled.

TABLE 1 Conventional Steels Embodiment of ATI 412 ™ Duracorr ® wt %Present Steel Alloy Alloy C 0.022  0.01-0.025  0-0.025 Mn 0.89 0.8-1 0-1.5 P 0.027   0-0.04  0-0.04 S 0.0014    0-0.004  0-0.015 Si 0.440.45-0.75 0-0.7 Cr 11.92 11.5-12  11-12.5 Ni 0.97  0.3-0.75 0-1  N 0.023  0-0.03  0-0.03 Mo 0.091  0-0.2 0.2-0.35  Cu 0.17 0.25 0 B 0.0003 0   0Annealing As-rolled 843° C. 766° C. 843° C. — temperature Brinellhardness 340 322 177 258 260-360  CVN at −40° C. 26-34 56-62 65-90  7-4915  (ft-lb) CVN (ft-lb) + 162-170 185-191 136-161 111-152 119-159  (0.4× HB)

The potential uses of alloys according to the present disclosure arenumerous. As described and evidenced above, the dual-phase stainlesssteels described herein are capable of being used in many applicationswhere abrasion resistance and/or wear resistance is important. Articlesof manufacture for which the steels according to the present disclosurewould be particularly advantageous include, for example, parts andequipment used in oil sands extraction and parts and equipment used insugar processing. Other applications for the stainless steels accoringto the present disclosure will be readily apprent to ordinarily skillpractitioners. Those having ordinary skill may readily manufacture theseand other articles of manufacture from the stainless steels according tothe present disclosure using conventional manufacturing techniques.

Although the foregoing description has necessarily presented only alimited number of embodiments, those of ordinary skill in the relevantart will appreciate that various changes in the alloys and article andother details of the examples that have been described and illustratedherein may be made by those skilled in the art, and all suchmodifications will remain within the principle and scope of the presentdisclosure as expressed herein and in the appended claims. For example,although the present disclosure has necessarily only presented a limitednumber of embodiments of stainless steels according to the presentdisclosure, and also has necessarily only discussed a limited number ofarticles of manufacture including the stainless steels, it will beunderstood that the present disclosure and associated claims are not solimited. Those having ordinary skill will readily identify additionalsteel compositions and may produce additional articles of manufacturealong the lines and within the spirit of the necessarily limited numberof embodiments discussed herein. It is understood, therefore, that thepresent invention is not limited to the particular embodiments disclosedor incorporated herein, but is intended to cover modifications that arewithin the principle and scope of the invention, as defined by theclaims. It will also be appreciated by those skilled in the art thatchanges could be made to the embodiments above without departing fromthe broad inventive concept thereof.

We claim:
 1. A dual-phase ferritic-martensitic stainless steelcomprising, by weight: about 11.5% to about 12% chromium; about 0.8% toabout 1.5% manganese; about 0.75% to about 1.5% nickel; 0% to about 0.5%silicon; 0% to about 0.2% molybdenum; 0% to about 0.0025% boron; iron;and Impurities; wherein the steel has a Brinell hardness (HB) and CharpyV-notch impact energy at −40° C. (CVN) such that CVN (ft-lb)+(0.4×HB) isabout 160 or greater.
 2. The dual-phase ferritic-martensitic stainlesssteel of claim 1, wherein molybdenum content is 0% to about 0.1%.
 3. Thedual-phase ferritic-martensitic stainless steel of claim 1, whereinnickel content is about 1.0% to about 1.5%.
 4. The dual-phaseferritic-martensitic stainless steel of claim 1, wherein manganesecontent is about 1.0% to about 1.5%.
 5. The dual-phaseferritic-martensitic stainless steel of claim 1, wherein boron contentis about 0.002% to about 0.0025%.
 6. The dual-phase ferritic-martensiticstainless steel of claim 1, wherein hardness of the steel is about 300HB or greater, and CVN of the steel is about 50 ft-lb or greater.
 7. Thedual-phase ferritic-martensitic stainless steel of claim 1, wherein thesteel has work hardenability up to a hardness of about 450 HB orgreater.
 8. The dual-phase ferritic-martensitic stainless steel of claim1 comprising, by weight: about 11.5% to about 12% chromium; about 1.0%to about 1.5% manganese; about 1.0% to about 1.5% nickel; 0% to about0.5% silicon; 0% to about 0.1% molybdenum; 0% to about 0.0025% boron; 0%to about 0.025% carbon; 0% to about 0.01% sulfur; 0% to about 0.03%nitrogen; iron; and impurities.
 9. The dual-phase ferritic-martensiticstainless steel of claim 8, further comprising at least one of copperand phosphorus.
 10. The dual-phase ferritic-martensitic stainless steelof claim 8, wherein the total concentration of carbon, nitrogen,phosphorus, and sulfur present is no greater than about 0.1%, by weight.11. The dual-phase ferritic-martensitic stainless steel of claim 8,wherein boron content is about 0.002% to about 0.0025%.
 12. Thedual-phase ferritic-martensitic stainless steel of claim 1, consistingessentially of, by weight: about 11.5% to about 12% chromium; about 0.8%to about 1.5% manganese; about 0.75% to about 1.5% nickel; 0% to about0.5% silicon; 0% to about 0.2% molybdenum; 0% to about 0.0025% boron; 0%to about 0.025% carbon; 0% to about 0.01% sulfur; 0% to about 0.03%nitrogen; optionally at least one of copper and phosphorus; iron; andimpurities.
 13. The dual-phase ferritic-martensitic stainless steel ofclaim 1, consisting essentially of, by weight: about 11.5% to about 12%chromium; about 1.0% to about 1.5% manganese; about 1.0% to about 1.5%nickel; 0% to about 0.5% silicon; 0% to about 0.1% molybdenum; 0% toabout 0.0025% boron; 0% to about 0.025% carbon; 0% to about 0.01%sulfur; 0% to about 0.03% nitrogen; optionally at least one of copperand phosphorus; iron; and impurities.
 14. The dual-phaseferritic-martensitic stainless steel of claim 1, consisting of, byweight: about 11.5% to about 12% chromium; about 0.8% to about 1.5%manganese; about 0.75% to about 1.5% nickel; 0% to about 0.5% silicon;0% to about 0.2% molybdenum; 0% to about 0.0025% boron; 0% to about0.025% carbon; 0% to about 0.01% sulfur; 0% to about 0.03% nitrogen;optionally at least one of copper and phosphorus; iron; and impurities.15. The dual-phase ferritic-martensitic steel of claim 1, consisting of,by weight: about 11.5% to about 12% chromium; about 1.0% to about 1.5%manganese; about 1.0% to about 1.5% nickel; 0% to about 0.5% silicon; 0%to about 0.1% molybdenum; 0% to about 0.0025% boron; 0% to about 0.025%carbon; 0% to about 0.01% sulfur; 0% to about 0.03% nitrogen; optionallyat least one of copper and phosphorus; iron; and impurities.
 16. Anarticle of manufacture including a dual-phase stainless steel as recitedin claim
 1. 17. The article of manufacture of claim 16, wherein thearticle of manufacture is selected from parts and equipment used in oilsands extraction and parts and equipment used in sugar processing. 18.An article of manufacture including a dual-phase stainless steel asrecited in claim
 12. 19. The article of manufacture of claim 18, whereinthe article of manufacture is selected from parts and equipment used inoil sands extraction and parts and parts and equipment used in sugarprocessing.
 20. An article of manufacture including a dual-phasestainless steel as recited in claim
 13. 21. The article of manufactureof claim 20, wherein the article of manufacture is selected from partsand equipment used in oil sands extraction and parts and parts andequipment used in sugar processing.
 22. An article of manufactureincluding a dual-phase stainless steel as recited in claim
 14. 23. Thearticle of manufacture of claim 22, wherein the article of manufactureis selected from parts and equipment used in oil sands extraction andparts and parts and equipment used in sugar processing.
 24. An articleof manufacture including a dual-phase stainless steel as recited inclaim
 15. 25. The article of manufacture of claim 24, wherein thearticle of manufacture is selected from parts and equipment used in oilsands extraction and parts and equipment used in sugar processing.